1. Field of the Invention
This invention relates to a damper which is mounted inside a hinge in order to prevent a cover, e.g. a keyboard cover of a piano, a seat of a toilet, from quickly and forcefully closing because of its own weight when a hand is moved off the cover or from falling while being open.
2. Description of Related Art
Some dampers for adjusting rotating torque of a shaft member include a valve mechanism between a shaft and a casing for varying in torque depending on a direction of rotating the shaft or the casing. However, the damper including the valve mechanism in the casing has a complicated structure, a higher number of parts, and a higher number of processing steps, which has poor productivity. For that, some dampers do not have a valve mechanism as illustrating in FIG. 9.
Referring FIG. 9, a damper has a casing 1, a rotating shaft 2 mounted in the casing 1, and a viscous fluid contained between the rotating shaft 2 and the casing 1. Based on a relative rotation of the rotating shaft 2 or the casing 1, the flow resistance occurring in a flow path is changed in value in order to change the rotating torque, resulting in the lessened impact.
As illustrated in FIG. 9, wings 13, 14 are formed on the rotating shaft 2. The rotating shaft 2 has outer diameters of which sizes are varied between the wings 13, 14.
The casing 1 has a largest inner diameter in the vertical direction of FIG. 9, and protrusions 15, 16 protrude inward from the inner face of the casing 1 in the lateral direction.
Therefore, as the rotating shaft 2 rotates in the direction of the arrow in FIG. 9 to allow the wings 13, 14 to approach the protrusions 15, 16, the flow paths 17, 18 between the leading ends of the respective wings 13, 14 and the inner periphery of the casing 1 are narrowed. This is because the wings 13, 14 move to the smaller portions of the inner diameter of the casing 1.
Further, as the larger diameter parts of the rotating shaft 2 also approach the protrusions 15, 16, the flow paths 19, 20 are also narrowed. Accordingly, with the rotation of the rotating shaft 2 in the direction of the arrow in FIG. 9, the rotating torque increases. It should be noted that, as in the above case, the torque increases when the rotating shaft 2 rotates from the state illustrated in FIG. 9 in the opposite direction of the arrow.
Specifically, in the event that the wing 13 moves in the range from the protrusion 16 to the protrusion 15, the rotating torque decreases gradually from a larger torque value, and then increases again. Then, the rotation stops when the wing 13 comes into contact with the protrusion 15.
Such a damper is used with a need for higher torque around the starting point and around the ending point of rotation to suppress an abrupt rotation, and for rotation with lower resistance in the middle.
The damper illustrated in FIG. 9 controls a magnitude of the rotating torque by use of flow resistance created between the inner periphery of the casing 1 and the wings 13, 14 or between the protrusions 15, 16 and the outer diameter face of the rotating shaft 2. The flow resistance depends on a sectional area of the flow path. For this reason, an inner diameter of the casing 1 and an outer diameter of the rotating shaft 2 are varied complicatedly. It is difficult to form parts in such complicated configuration. This produces difficulties in forming the casing 1 and the rotating shaft 2 with accuracy. If each of the parts does not have a constant configuration, the assembled damper can not have constant rotating torque.
Even under a condition that the casing 1 and the rotating shaft 2 are both fabricated with accuracy, if the assembly of the casing 1 and shaft 2 has backlash, a dimension of the flow path will be warped. Likewise, the aimed torque cannot be obtained.
In order to control the rotating torque, there is a need to strictly manage the accuracy of finishing and the accuracy of assembling.
Further, in order to adjust the torque to any given value, there is a need to change molds, resulting in an increase in cost.
Alternatively, there is another manner in which fluid such as oil is changed in viscosity to adjust the torque. However, an arbitrary torque cannot be obtained unless oils or the like having different viscosities are blended. In this manner, there is a need to prepare a large number of kinds of oils or the like having different viscosities, resulting in high costs. Further, considerable effort is spent on the choice of proportion of the oil or the like to obtain a required torque.
It is an object of the present invention to provide a damper having a simple structure and allowing the setting of arbitrary torque with smooth reproducibility.
It is another object of the present invention to provide a method of fabricating a damper having arbitrary torque at low cost.
A damper according to a first aspect of the present invention features a configuration including: a shaft member having a shaft and wings formed on the outer periphery of the shaft; a cylindrical casing relative-rotatably incorporating the shaft member; an oil chamber provided between the outer periphery of the shaft member and the inner periphery of the casing; a protrusion provided on the inner periphery of the casing and slidable on the outer periphery of the shaft; a communicating path passed through the shaft to make the communication between a pair of the adjacent oil chambers out of all the oil chambers individually surrounded by the wings and the protrusions, and having at least one of openings which is to be closed by the protrusion, provided on the casing, within a relative-rotating range of the shaft member.
A second aspect of the present invention features in that one of the openings of the communicating path is formed at a position allowing the one opening to open toward the oil chamber at all times within the relative-rotating range of the shaft member.
According to the second aspect, the shaft member has higher rotating torque only in a region of the rotating range of the shaft member than that in other regions thereof. For example, using such damper for a keyboard cover of a piano, the damper is adapted such that the high-torque region of the rotating range is produced before the cover is closed. Thus, the cover can be prevented from quickly and forcefully closing because of its own weight even after a hand is moved off the cover.
A third aspect of the present invention features in that the protrusions provided on the casing independently close the openings of both ends of the communicating path within the relative-rotating range of the shaft member.
According to the third aspect, it is possible to set the two high-torque regions within the rotating range of the shaft member. This allows, for example, the cover of the piano to independently keep its upright position when the cover is fully opened, and not to fall with a bang at the final time of closing the cover.
A fourth aspect of the present invention features in that the protrusion provided on the casing closes the opening of the communicating path at either one or both of the starting and ending points of a relative rotation of the shaft member.
According to the fourth aspect, it is possible to set the high-torque regions at the starting point and the ending point of rotation.
A fifth aspect of the present invention features in that a plurality of the communicating paths are provided between the pair of adjacent oil chambers.
According to the first aspect to the fifth aspect of the present invention, it is possible to provide a damper having a simple structure and allowing the setting of arbitrary torque with smooth reproducibility.
According to the fifth aspect, it is possible to control a sectional area of the oil flow path by changing the number of communicating paths. For example, if a sectional area of the flow path is adjusted based on the number of communicating paths, the individually communicating paths can be equal in diameter. In this event, varying sectional areas of the flow path can be achieved without changing sizes of perforating tools such as a drill.
A method of fabricating a damper according to a sixth aspect of the present invention features the steps of: molding a cylindrical casing and a shaft member having wings with use of a mold or die; opening a communicating path through the shaft member with use of a perforating tool; and mounting the shaft member in the casing.
According to the sixth aspect, the torque can be changed without changing molds or dies. Therefore, the dampers having arbitrary torque can be fabricated at low cost.